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Oligodendrogliomas are the third most common glioma, accounting for 2-5% of all primary brain tumours and 5-18% of gliomas. They are more common in adults, particularly in people aged 40-60.

Oligodendrogliomas are primary brain tumours which means they have originated in the brain instead of spreading from elsewhere. They belong to the group of brain tumours known as gliomas as they develop from a type of glial cell known as an oligodendrocyte.

Oligodendrocyte cells produce a fatty, protective covering (called myelin) of the nerve cells in the brain, which helps nerve signals to travel along the nerves more quickly.

Oligodendroctye Cells:: Oligodendrocyte Cells:

What causes oligodendrogliomas?

As with most tumours, the cause is not known. This can be a difficult thing to accept and can leave you feeling helpless, but there is nothing you could have done to prevent this from happening.

The Brain Tumour Charity is contributing to the funding of research into a possible cause that is focussed around our genes.

What are the symptoms of an oligodendroglioma?

A person with an oligodendroglioma may display one or more of these symptoms:

  • Seizures
  • Headaches (not alleviated by pain killers and are worse in mornings associated with nausea and vomiting)
  • Mental status change (general changes in brain function)
  • Vertigo or nausea
  • Visual loss (altered vision or visual hallucinations)
  • Muscular weakness and loss of control of bodily movements (weakness down one side of body)
  • Altered sensations (strange smells, hallucinations relating to sense of smell)

Sometimes the symptoms experienced depend on where the brain tumours are located. If they are in the frontal lobe this may cause gradual changes in mood and personality, weakness or numbness in muscles of one side of the body.

If it is located in the temporal lobe, this may cause problems with speech and coordination or it may affect memory.

What are the types of oligodrendroglioma?

Oligodendrogliomas are divided into two grades:

  • Grade 2 (low grade) oligodendrogliomas are very slow growing
  • Grade 3 (high grade) anaplastic oligodendrogliomas are a faster growing and malignant type

The majority of oligodendrogliomas occur in the frontal lobe, and the second most common site affected is the temporal lobe.

Grade 3 oligodendrogliomas are more common in older people aged 60-80, but can affect any age. Oligodendrogliomas are slightly more common in men than in women.

Occasionally oligodendrogliomas contain clear evidence of different glial cells called astrocytes. These tumours which have a mix of cells may be referred to as 'oligoastrocytomas'. However, this diagnosis is discouraged because genetic testing can now determine whether the tumour should be classified as an astrocytoma or an oligodendroglioma.

Biomarker tests for Oligodendrogliomas

A biomarker is a biological marker or indicator of a certain process happening in the body. If you have a brain tumour, a biomarker test may be used to look at the genes associated with your type of tumour.

With brain tumours, biomarker tests can be used to see if your tumour has certain changes in its genes that may be used to:

  • help diagnose the type of tumour you have 
  • predict how fast your tumour will grow
  • suggest how you may respond to certain treatments, such as chemotherapy and, possibly, radiotherapy.

Quite often biomarker testing is done routinely, so you may not be consulted before this is done. You can, of course, choose not to be told the result.

Ask your healthcare team if testing is done routinely and, if it’s not, think about it carefully and discuss it with them and your family before deciding whether to ask for it.

1p/19q co-deletion test

What is the 1p/19q test?

The 1p/19q test may predict long-term survival in people who have oligodendroglioma.

The test can also be useful in diagnosing oligodendrogliomas and, therefore, in making decisions about the most appropriate treatment for you.

How does the test work and what does it show?

Our bodies are made up of cells. Each cell has 23 pairs of chromosomes, which carry your genes (DNA). One chromosome of each pair is inherited from your mother, and the other from your father. Each pair of chromosomes are numbered 1 to 22, then XX or XY.

The 1p/19q test looks at genetic changes to chromosomes 1 and 19 to see whether they have a section missing. If the sections called the p section of chromosome 1 and the q section of chromosome 19 are missing, this means that the genes carried in those sections are also missing. 

These genes seem to be involved in resistance to chemotherapy drugs. So if you’re found to be missing both those sections, you’re more likely to have a better response to chemotherapy and longer overall survival.

IDH1 and IDH2 mutation test

What is the IDH1/IDH2 test?

The IDH1/IDH2 test may predict long-term survival in people who have oligodendrogliomas.

It may also be useful in predicting how effective a particular treatment is likely to be.

How does the test work and what does it show?

IDH1 and IDH2 are genes. A change (mutation) in the IDH1/IDH2 genes has been found in about 80% of astrocytomas, oligodendrogliomas and secondary glioblastomas.

Tumours that have the change are known as IDH–mutant, and those without the change are known as IDH-wildtype.

For people with high grade types of these glioma, those whose tumours are IDH-mutant tend to have better long-term survival rates than those who are IDH-wildtype.

It’s not yet clear how mutations of the IDH1/IDH2 genes link to outcomes for people with low grade brain tumours - both in terms of long-term survival and also treatment outcomes. However, there’s some evidence that, similar to high grade gliomas, people whose tumours are IDH-mutant have better long-term survival rates than those who are IDH-wildtype.

Further research needs to be carried out before clear conclusions can be drawn, but it may be that chemoradiotherapy (a combination of chemotherapy and radiotherapy) is more effective for some people with grade 2 gliomas who have the IDH1/IDH2 mutation, than those who don’t. (See TP53/ATRX mutations section further on.)

It’s important to be aware that people with gliomas that have the IDH1/IDH2 mutation tend to be younger adults and older children, which may partially account for their longer survival.

MGMT promoter methylation test

What is the MGMT methylation test?

For people with anaplastic oligodendroglioma, the MGMT methylation test helps to predict how effective chemotherapy treatment is likely to be, although there are many other factors that also affect response to treatment. This can be used to help plan a suitable, individualised treatment plan.

What does the test show?

In summary, the test looks at the amount (percentage) of something called methylation. If your tumour is found to be:

  • MGMT methylated, you’re more likely to respond well to TMZ chemotherapy.
  • MGMT unmethylated, you’re less likely to respond to TMZ chemotherapy.

This helps your healthcare team decide on the best course of treatment for you. For example, if your tumour is unmethlyated, giving you high doses of chemotherapy may give you lots of unpleasant side-effects, but with little benefit in terms of reducing your tumour.

If you do decide to have the test, you need to be aware that it may be found to be unmethylated. Speak to your healthcare team about what would happen next if this turned out to be the case.

There are other factors that influence the effectiveness of chemotherapy, so there’ll always be ‘good’ and ‘poor’ responders in both the methylated and unmethylated groups.

TERT promoter mutation test

TERT promoter mutation test

When found with 1p/19q co-deletion and IDH-mutant biomarkers, the TERT promoter mutation suggests a diagnosis of oligodendroglioma, and predicts greater benefit from chemotherapy and radiotherapy and longer survival, particularly in grade 2 and 3 gliomas.

However, when the TERT mutation is found on its own in grade 2 and 3 gliomas, it predicts poorer survival. This suggests the need for early, more aggressive treatment.

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